How to correct the 'IOError: [Errno 6]' when I want to get IP address using python script?

Question

when I use this python script to get my OSX IP addr,always hit IOError: [Errno 6] Device not configured, and not get the point of this problem.

 import socket
    import fcntl
    import struct
    def get_ip_address(ifname):
        s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
        return socket.inet_ntoa(fcntl.ioctl(
            s.fileno(),
            0x8915,  # SIOCGIFADDR
            struct.pack('256s', ifname[:15])
        )[20:24])
    get_ip_address('lo')
    # '127.0.0.1'
    get_ip_address('eth0')
    # '38.113.228.130'
    get_ip_address('ppp0')
    # '123.163.166.00'

thanks for your help. Frank